This page provides a table for sample size comparing two survival rates using the Kaplan Meier Log Rank Test.

The table provides sample size (per group) for powers of 0.8, 0.9, and 0.95, Probability of Type I Error (α)
of 0.1, 0.05, and 0.01, and for the one and two tail model. The survival rates are from 0.02 (2%) to 0.98 (98%) at
0.02 (2%) intervals

When there is more than two groups, the sample size should be the same as for two groups, but the two tail model should
be used. The two survival rates should be the narrowest anticipated ot to be detected between any of the two groups.

Abbreviations are :

α = Probability of Type I Error

Power = 1=β

s1 and d2 = Survival Rate of two groups being compared

1Tail and 2Tail are sample size (per group, assuming equal sample size groups) for the one and two tail model

In the table, the sample size is that for each of two groups, assuming that the sample size in the two groups are same or at
least similar. This allows a quick reference for planning purposes.

The sample size calculated from the program in Sample Size for Survival (Kaplan Meier Log Rank Test) Program Page
is that for both groups combined,
allowing for a large difference between the sample size between the two groups. This flexibility is needed when the index
cases are more difficult to come by, so that an index case is often matched by 2 to 3 background cases (as is in the case
of cancer).